1. Technical Field
The present invention relates to a test apparatus and a test method. Particularly, the present invention relates to a test apparatus and a test method for testing a device under test including a receiving circuit for receiving signals transmitted through a communication cable.
2. Related Art
FIG. 1 shows communication devices 210 and 220, and a communication cable 200 corresponding to 10Gbase-T. Recently, it has been made advance to standardize 10Gbase-T (IEEE802.3an) being capable of speedily transmitting at 10 Gbps as a next-generation Ethernet (registered trademark) standard. A communication network system corresponding to the 10Gbase-T can communicate by connecting a four-line twisted-pair communication cable 200 with the maximum length of 100 m between a transmitting circuit 230 and a receiving circuit 240. In addition, there are the following prior art documents related to a signal generation, which are U.S. Patent Application Publication No. 2005/0174926 and U.S. Pat. Nos. 3,952,189 and 6,369,735.
FIG. 2 is a view exemplary showing a frequency characteristic of gain of the communication cable 200 corresponding to 10Gbase-T. Here, testing a communication device, a test apparatus generates a signal waveform to be received by the receiving circuit through the communication cable using a DA converter and outputs the generated signal waveform as a test signal. For example, as for the signal passed through a 100 m length of the communication cable 200 corresponding to the 10Gbase-T, as shown in FIG. 2, the frequency component in 400 MHz frequency band is attenuated to around 1/20- 1/50, and if the quality of cable is not good, the frequency component is further attenuated to about 1/100. As thus described above, the test apparatus generates a test signal of which high-frequency component is significantly attenuated when the test apparatus tests the communication device 220 corresponding to the Gbase-T.
In this case, the test apparatus should have had accuracy more than the predetermined bit number in the entire frequency band and have included a DA converter with a high-bit resolution than the bit number for the accuracy necessary to indicate the signal waveform when the test apparatus outputs the test signal of which high-frequency component is significantly attenuated. For example, if the test apparatus outputs a signal waveform of which low-frequency component is not attenuated and of which high-frequency component is attenuated to 1/100 at six-bit accuracy in the entire frequency band, the test apparatus should have a DA converter having 12˜13-bit resolution obtained by adding the bit number (6 bits) for the accuracy necessary to indicate the waveform and the bit number (6 to 7 bits) for the attenuation to 1/100. However, such DA converter with the high resolution is very expensive and large in size.
Thus, an object of the present invention is to provide a test apparatus and a test method being capable of solving the problem accompanying the conventional art. This object is achieved by combining the features recited in independent claims. Then, dependent claims define further effective specific example of the present invention.